JPH11268101A - Method for producing thermoplastic resin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a thermoplastic resin film in which a discharge electrode can be automatically adjusted to an appropriate range position in which a good molding state can be obtained in a short time, including its direction, with less material loss and improved productivity. Method. SOLUTION: A molten thermoplastic resin is extruded into a film from a die, extruded and dropped on a cooling rotary drum,
An electrostatic charge is applied to the film by a linear discharge electrode provided in the width direction in the vicinity of the surface of the cooling drum, and the film is transferred while being brought into close contact with the cooling drum while the film is solidified. In a method of manufacturing a thermoplastic resin film for adjusting a circumferential position of a cooling rotary drum of the discharge electrode based on a current flowing through the electrode, the discharge electrode is formed based on an intensity of an electromagnetic wave generated by a discharge from the discharge electrode. A method for producing a thermoplastic resin film, comprising adjusting a direction with respect to a falling film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a thermoplastic resin film. More specifically, the present invention relates to a method for producing a thermoplastic film having less unevenness in thickness and surface defects and excellent surface properties.

[0002]

2. Description of the Related Art As is well known, a thermoplastic resin film (also called a sheet) is formed into a film by forming a molten thermoplastic resin into a film from a slit-shaped die and extruding the film onto a cooling rotary drum. It is manufactured by performing necessary processing such as stretching. At the time of this forming, a wire electrode, which is a discharge electrode to which a high voltage is applied, is disposed over a substantially entire width of the film at a predetermined position in a space above the film on the cooling rotary drum, thereby electrostatically charging the film. It has been conventionally known that the degree of adhesion to the cooling rotary drum can be improved and a good molding state can be obtained.

[0003] That is, a minute current flows from the wire electrode to the cooling rotary drum side, and the thermoplastic resin is pressed against the cooling rotary drum by the electrostatic force generated at that time, and the air is caught between the film and the cooling rotary drum. In addition to this, the cooling efficiency is improved and the formability is improved.

By the way, in order to obtain the above-mentioned good molding state in this method, the position of the wire electrode is an important condition. In other words, of the positional relationship between the wire electrode and the surface of the cooling rotary drum, for the distance to the surface,
There are the following problems. If this interval is too large, the potential gradient between the wire electrode and the cooling drum is reduced, and sufficient electric charge is not released from the wire electrode. Sufficient adhesion cannot be obtained. On the other hand, if the interval is too small, the potential gradient becomes too large, causing dielectric breakdown in the film, causing defects such as pinholes, and causing a discharge in an uneven portion of the wire electrode, causing the power supply to drop and the manufacturing process to proceed. Adversely affect

[0005] In addition, the position of the rotating direction of the rotating drum for cooling the wire electrode, that is, the position of the film feeding direction,
There are the following problems. The film discharged from the base is taken off by the surface of the cooling drum that rotates at a predetermined speed in a state of natural fall, and the wire electrode is installed upstream from this direction with reference to the normal direction at the ground point where the film is grounded. Then, the film is pressed against the cooling drum before landing on the surface of the cooling drum in a naturally falling state, so that the film is not stable and is likely to vibrate or shake. And surface defects.

Conversely, if the film is installed downstream of the normal direction, the cooling drum side of the film is cooled and solidified to some extent at the point closest to the wire electrode where a large pressing force acts. Air is caught between the drum and the drum, causing bubbles and surface defects.

Therefore, the optimum position of the wire electrode in the film feeding direction is at or immediately before the landing point on the surface of the cooling rotary drum in the state of natural fall without the action of external force such as electrostatic force of the film. In other words, a film having a stable landing and a good molding surface, that is, a film having good surface properties can be obtained by being installed at that position.

However, this landing point is determined by the relationship between the plasticity of the discharged film and the rotation speed of the cooling rotary drum. If there is a large variation in manufacturing conditions, the position of the discharge electrode becomes inappropriate, and A drawback arises, and there is a problem that it takes time to adjust. In particular, the change of the product brand is remarkable, and there is a problem that it takes a lot of time to search for the optimum position of the discharge electrode.

Further, the film extruded from the slit-shaped die is narrower than the width of the die due to the neck-in phenomenon, and both ends of the film become thicker due to the shrinkage. For this reason, the film landing point is not parallel to the axis of the cooling rotary drum at a part of the width direction, specifically at both ends, which also makes it difficult to find the optimum position of the discharge electrode. I was

On the other hand, a method for automatically positioning a wire electrode has been proposed. For example, JP-A-60-120
Japanese Patent Application Publication No. 028 proposes a method of automatically controlling the position of the wire electrode so that the current flowing therethrough becomes a maximum value while keeping the distance from the cooling rotary drum constant. Also,
Japanese Patent Application Laid-Open No. 4-83627 proposes a method of adjusting the position of a discharge electrode, that is, a wire electrode, so that the current fluctuation width of the discharge current is minimized while keeping the distance from the cooling rotary drum constant. .

[0011]

In the above-mentioned conventional method,
The detection signal used for automatic adjustment of the position of the wire electrode is 1
Therefore, there is a problem that the right and left balance cannot be adjusted in the die width direction. The present invention has been made in order to solve this problem. The discharge electrode can be automatically adjusted to an appropriate range position in which a good molding state can be obtained in a short time, including its direction, with less material loss and improved productivity. It is an object of the present invention to provide a method for producing a thermoplastic resin film.

[0012]

The above object is achieved by the present invention described below. That is, the present invention provides a method in which a thermoplastic resin in a molten state is extruded into a film from a die and dropped on a cooling rotary drum, and the film is formed by a linear discharge electrode provided in the width direction near the surface of the cooling rotary drum. Applying an electrostatic charge to the film, while transporting the film in close contact with the cooling drum, and solidifying the film, the position of the discharge electrode in the circumferential direction of the cooling drum is determined based on the current flowing through the discharge electrode. In the method for producing a thermoplastic resin film to be adjusted, a method for producing a thermoplastic resin film characterized by adjusting a direction of a discharge electrode with respect to a falling film based on the intensity of electromagnetic waves generated by discharge from the discharge electrode. is there.

According to the present invention described above, it has been found that the degree of deflection from the direction in which the discharge electrode falls to the film, specifically, the direction parallel to the film can be detected by the distribution of the electromagnetic wave intensity in the film width direction. What was done. As described above, the present invention adjusts the circumferential position of the cooling rotary drum of the discharge electrode according to the value of the current flowing through the discharge electrode, and adjusts the direction of the discharge electrode according to the intensity of electromagnetic waves generated by the discharge from the discharge electrode. Therefore, the problem of the conventional example is solved.
In addition, it can be manufactured with high productivity.

In the present invention, for the purpose, in the method of adjusting the position of the discharge electrode in the circumferential direction of the cooling rotary drum, the above-described current value itself or its fluctuation value in the conventional example is used, and these are set to predetermined values. An adjustment method can be applied. However, the method of adjusting the position of the discharge electrode so that the current value of the frequency component of the predetermined frequency range of the discharge current shown in the examples described below is within the set range can detect film thickness variation with high sensitivity, and the control system is accordingly limited. It is preferable in that improved surface properties can be obtained. The predetermined frequency depends on the process to be applied, but empirically is usually 3 to 15 Hz.

According to the method of adjusting the direction of the discharge electrode based on the intensity of the electromagnetic wave, which is a feature of the present invention, the degree of parallelism of the discharge electrode with the falling film is detected based on the intensity of the electromagnetic wave in the width direction of the film so that the discharge electrode can be adjusted to be parallel. It is not particularly limited as long as it is one. Specifically, a method of adjusting the direction of the discharge electrode so that the maximum value of the intensity of the electromagnetic wave at both ends in the film width direction is preferably applied from the viewpoint of detection sensitivity. Among them, a method in which the positions of both ends of the discharge electrode are adjusted by equal amounts in opposite directions to each other is preferable, since only the direction can be adjusted without changing the circumferential position of the discharge electrode.

Further, from the viewpoint of control stability, the method of moving the discharge electrode is preferably a method in which the discharge electrode is moved along the surface while maintaining a constant distance from the surface of the cooling drum. Furthermore, in the actual operation, from the aspect of product quality stability, the position adjustment is automatically adjusted at the time of start-up from the start of production to the steady operation and at the time of shutdown from the steady operation to the end of production,
It is preferable to use an operation method in which the position is not automatically adjusted during the steady operation, and only the thickness, the number of defects, or the quality-related variables such as the above-mentioned current and electromagnetic waves are monitored.

In the present invention, as described above, the circumferential position control system analyzes the frequency component of the detected current flowing through the discharge electrode, and uses the position adjustment device to adjust the position of the discharge electrode based on the data. The method for adjusting the position of the discharge electrode is such that the position of the discharge electrode is temporarily changed by a position adjustment device to a position outside a normal operation range where a large thickness variation occurs, and then the change is performed. A method of adjusting the current value of the component in the frequency range at a predetermined speed in the direction opposite to the direction until the current value reaches a predetermined value set in advance is preferable from the viewpoint of control stability. Hereinafter, the details of the present invention will be described.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The thermoplastic resin in the present invention comprises:
In general, it includes all resins that can be formed into a film (also referred to as a sheet). Representative examples of these thermoplastic resins include polyesters such as polyethylene terephthalate and polyethylene naphthalate, and polyolefins and polyamides. Further, these copolymer mixtures may contain other additives and the like. Further, the film extruded from the die may be a single-layer film or a multilayer film in which the same or different resin layers are laminated in a plurality of layers.

The discharge electrode only needs to be made of a linear conductive material, and a wire electrode made of a metal wire is usually used. Since a high DC voltage is normally applied to the discharge electrode, this current value is usually detected by a DC ammeter, but AC is used to adjust the position of the discharge electrode based on the result of analyzing the frequency component of the current value. There is no problem with the ammeter.

The apparatus for analyzing the frequency component of the current value may be a commercially available frequency analyzer, but it may be subjected to a fast Fourier transform (FFT) using a commercially available personal computer.
) Can be calculated at a speed sufficient for adjusting the position of the discharge electrode even if the calculation is performed using software capable of executing the above.

As a device for measuring the intensity of the electromagnetic wave generated by the discharge from the discharge electrode, a commercially available electromagnetic wave measuring device can be used satisfactorily, and a device capable of measuring up to 3 GHz is preferable. Further, even if a magnetic field measuring device having a correlation with an electromagnetic wave is used, the object can be achieved, and the device can be constructed at a relatively low cost. The intensity distribution measurement in the film width direction is performed by scanning the electromagnetic wave measuring device in the width direction. Once the measurement positions are determined, it is preferable to install an electromagnetic wave measurement device at each position to perform continuous measurement. Hereinafter, embodiments of the present invention will be described.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of the structure of a film forming section of a thermoplastic resin film manufacturing apparatus for implementing the method of the present invention and a position control device for a discharge electrode thereof. As shown in the figure, a thermoplastic resin is melted and extruded from a die 1 to form a film 4 which falls on the surface of a cooling rotary drum 3 rotating at a predetermined speed, and is cooled and solidified while being transferred by this. It is transferred to the omitted next stretching step. Here, the discharge electrode 2 made of a metal wire is connected to a high voltage generator 8 and is maintained at a high voltage. As a result, an electrostatic charge is induced in the film 4 and the film 4 is a counter electrode for cooling. It is closely attached to the rotating drum 3.

In this embodiment, a position adjusting device (not shown) is provided which can move the position of the discharge electrode 2 as shown by an arrow in the figure while maintaining a constant distance from the cooling rotary drum 3 and install it there. doing. This position adjusting device can operate the left and right ends of the discharge electrode 2 independently in the width direction of the film.

An ammeter 5 is connected between the discharge electrode 2 and the high voltage generator 8 so that the current flowing through the discharge electrode 2 can be constantly measured. The current flowing through the discharge electrode 2 detected by the ammeter 5 is input to the frequency analyzer 6.
The frequency analysis device 6 analyzes the frequency of the input current,
An output signal proportional to the frequency component in the set frequency range is output to the controller 7. The controller 7 outputs a control signal for moving the discharge electrode 2 in a predetermined direction at a predetermined speed to the position adjusting device based on the output signal, and the position adjusting device cools the position of the entire discharge electrode 2 according to the control signal. The distance from the rotary drum is kept constant, and the distance is adjusted in the direction of the arrow in the figure.

The electromagnetic wave measuring device 9 is installed on a scanning means for moving the cooling rotary drum 3 (not shown) in the width direction thereof in parallel with the axis of the cooling rotary drum 3. Is detected by scanning the space in the vicinity of, detecting intensities at predetermined measurement positions in the width direction of the electromagnetic waves generated by the discharge from the discharge electrode 2, and sequentially outputting them to the controller 7. The measurement position of the electromagnetic wave measuring device 9 may be any position at which the electromagnetic wave due to the discharge can be detected, but is usually measured in the space between the discharge electrode 2 and the falling film or in the vicinity thereof as shown in the figure. The controller 7 outputs a direction control signal for finely adjusting one of the positions of both ends of the discharge electrode 2 to the position adjustment device based on the detection signal. One or both end positions may be moved to adjust the direction.

A control method using the above configuration will be described. As shown in FIG. 1, the film 4 extruded from the die 1 has a fixed distance between the die 1 and the cooling rotary drum 3, and adheres to the cooling rotary drum 3 by electrostatic force generated by the discharge electrode 2. Until the edge portion is opened, the edge portion is in an unstable state because it is open. As described above, the discharge electrode 2
When the discharge electrode 2 is moved closer to the film 4 when the film 4 is moved near the ground point where the film 4 comes into contact with the surface of the cooling drum 3 by natural fall, the film 4 is moved by the reaction force of the electrostatic force.
Vibration starts from the edge portion between the die 1 and the cooling rotary drum 3. When the distance is further reduced, the entire film 4 between the die 1 and the cooling rotary drum 3 starts to vibrate, which causes unevenness in thickness and defects in the film.

Since the distance between the film 4 and the discharge electrode 2 changes when the film 4 vibrates, the electrostatic force changes, and the current flowing through the discharge electrode 2 also changes with the die 1 and the cooling rotary drum 3. It fluctuates at the frequency of the vibration of the edge portion between them. Therefore, the above-mentioned vibration of the film 4 can be detected by detecting the current value of the component in the specific frequency range. Therefore, the discharge electrode 2 is moved with respect to the film 4 while keeping the distance between the discharge electrode 2 and the cooling rotary drum 3 constant, and a frequency component in which the current value fluctuates is detected by the frequency analysis device 6, and the frequency component is determined to be a specific frequency. If the position of the discharge electrode 2 is adjusted so as to be equal to or less than a set range, for example, a specific size, the vibration of the film 4 can be set to a range where there is no problem in practical use, and a film having the above-mentioned defects and good surface properties can be obtained.
The goal can be reached.

However, if the ground line between the discharge electrode 2 and the rotating drum 3 for cooling the film 4 is not parallel, the current value may fluctuate due to vibration of only one side of the film edge. Can not reach. On the other hand, since the deviation can be detected by the intensity of the electromagnetic wave in the width direction of the film 4, the distribution of the electromagnetic wave intensity in the width direction of the cooling drum 3 is detected by the above-described electromagnetic wave measuring device 9, and both ends in the width direction are detected. This can be avoided by finely adjusting the position of one or both ends of the discharge electrode 2 so that the intensity of the electromagnetic waves in the electrodes is balanced, or more specifically, equal. Thus, a film 4 having excellent surface properties can be manufactured.

Hereinafter, an example in which a polyethylene terephthalate film is manufactured by the above apparatus will be described. The polyethylene terephthalate resin is melted by being extruded from an extruder (not shown), and has a lip opening of 2 mm and 285 ° C.
Extruded from the die 1 set to a thickness of 100
A μm polyethylene terephthalate film 4 was formed. At that time, a voltage of 6.5 KV was applied to the discharge electrode 2. The position adjusting device was set so as to move the discharge electrode 2 while keeping the distance from the surface of the cooling rotary drum 3 at 4 mm. In addition, as shown in FIG. 2, the discharge electrode 2 is provided with an insulating cover 2a other than the portion facing the film 4 so as to prevent unnecessary discharge.

The production was performed as follows. The position of the first discharge electrode 2 is set to a position downstream of the point where the film 4 comes into contact with the cooling rotary drum 3 and outside the normal operating range, which has a defect caused by air entrapment on the entire surface. Started automatic adjustment. The movement of the discharge electrode 2 is 0.1
The measurement was performed at a low speed of mm / s. This was set by sufficiently considering the response time at which the edge portion of the film 4 starts vibrating due to the reaction force of the electrostatic force of the discharge electrode 2.

The frequency analysis device 6 is provided with a filter,
The frequency component of the power supply and the frequency component caused by the eccentricity of the cooling rotary drum are cut. In the automatic adjustment by the current, the frequency analysis device 6 was set to measure a component having a frequency of 10 Hz or less, and the movement of the discharge electrode 2 was stopped when the output increased to three times the initial state. The discharge electrode 2 moved from the initial position to the upstream side with respect to the traveling direction of the film 4 in parallel with the axis of the cooling drum 3. Following this movement, the output from the frequency analyzer 6 gradually increased, and stopped when it became three times the set value.

The result of measurement of the electromagnetic wave generated by the discharge from the discharge electrode 2 in the width direction of the discharge electrode 2 by the electromagnetic wave measuring device 9 at this position is as shown by the broken line in the graph of FIG.
This graph shows the distribution of the electromagnetic wave intensity in the width direction in the front view shown in the upper part of FIG. 2 when the cooling rotary drum 3 is viewed from the direction of the arrow 10 in FIG. The ratio of the electromagnetic wave intensity on the right side from the center was reduced by 10%. In this distribution, it is determined that the right end having a relatively small electromagnetic wave intensity is relatively far from the film 4 falling from the left end.

The controller 7 calculates the amount of movement of each end, that is, the direction control signal, based on the difference of each end from the average of the two, specifically 5%, so as to make this difference zero, Output to the position adjustment device to automatically adjust the end position. By adjusting both ends in the opposite direction in this manner, the direction of the discharge electrode 2, specifically, the parallelism with the falling film 2 is adjusted without substantially changing the entire position of the discharge electrode 2. Can be adjusted quickly. In this example, as a result of the adjustment, the intensity of the electromagnetic wave was balanced as shown by the solid line in FIG. 2, and the adjustment was stopped at this position, resulting in a steady operation. As a result of the adjustment, the discharge electrode 2 is arranged such that the left end of the discharge electrode 2 is 0.1 mm downstream and the right end is 0.1 mm upstream of the discharge electrode 2 before adjustment. He was moving at a constant distance.

By the above adjustment, as shown by the solid line in the graph of FIG.
In other words, the falling film 4 and the discharge electrode 2 are parallel,
In addition, the discharge electrode 2 could be automatically adjusted to a position where there is little vibration, in other words, a position that is optimal for the production of the film 4 having no defects and having a stable film thickness.

It is also possible to detect the current and the electromagnetic wave of the constant discharge electrode 2 and to adjust and control the position of the constant discharge electrode 2. However, once it is in a steady operation, it is relatively stable, and the delicate movement of the discharge electrode 2 due to the control sometimes affects the characteristics of the film 4 and may cause defects such as uneven thickness. In the present example, once adjusted to the optimal position, the adjustment control is performed only when the quality of the defect or the like exceeds a predetermined reference level. In other cases, a necessary quality-related variable such as a thickness or a defect is used. Alternatively, an operation method in which only the above-described current, electromagnetic wave, or the like, specifically, a defect detector is monitored by a defect detector is used. According to this example, the number of adjustment steps for changing brands was reduced by 10%, and the unevenness of thickness unevenness in the width direction of the film was reduced, so that the process was stabilized and the productivity was improved by 10%.

[0036]

According to the present invention, it is possible to automatically and automatically adjust the discharge electrode to the optimum position range in a short time including the parallelism with the film to fall, thereby reducing the raw material loss and improving the productivity. Further, it is possible to stably obtain a film having excellent surface properties without variation in surface defects in a film as a product. As described above, the present invention greatly contributes to cost reduction, productivity improvement, quality improvement, and the like of the thermoplastic resin film.

[Brief description of the drawings]

FIG. 1 is an explanatory view of the configuration of a film forming section of a thermoplastic resin film manufacturing apparatus and a discharge electrode position control device thereof for implementing a method of the present invention.

FIG. 2 is a measurement example of an electromagnetic wave intensity distribution measured in a width direction of a film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Die 2 Discharge electrode 3 Rotating drum for cooling 4 Film 5 Ammeter 6 Frequency analysis device 7 Controller 8 High voltage generator 9 Electromagnetic wave measurement device

Claims (9)

[Claims] 1. A molten thermoplastic resin is extruded into a film from a die and extruded and dropped on a cooling rotary drum.
An electrostatic charge is applied to the film by a linear discharge electrode provided in the width direction in the vicinity of the surface of the cooling drum, and the film is transferred while being brought into close contact with the cooling drum while the film is solidified. In a method of manufacturing a thermoplastic resin film for adjusting a circumferential position of a cooling rotary drum of the discharge electrode based on a current flowing through the electrode, the discharge electrode is formed based on an intensity of an electromagnetic wave generated by a discharge from the discharge electrode. A method for producing a thermoplastic resin film, comprising adjusting a direction with respect to a falling film. 2. The method for producing a thermoplastic resin film according to claim 1, wherein the position of the discharge electrode is adjusted so that a current value of a frequency component of a predetermined frequency range of the discharge current falls within a set range. 3. The method for producing a thermoplastic resin film according to claim 2, wherein said predetermined frequency is 3 to 15 Hz. 4. The method for producing a thermoplastic resin film according to claim 1, wherein the direction of the discharge electrode is adjusted so that the maximum value of the intensity of the electromagnetic wave at both ends in the film width direction is equal. 5. The method for producing a thermoplastic resin film according to claim 4, wherein the positions of both ends of the discharge electrode are adjusted by equal amounts in directions opposite to each other. 6. The discharge electrode is moved along a surface of the cooling drum while maintaining a constant distance from the surface.
6. The method for producing a thermoplastic resin film according to any one of items 5 to 5. 7. Automatic adjustment of the position adjustment at the start-up from the start of production to the steady operation and at the time of the fall from the steady operation to the end of the production. The method for producing a thermoplastic resin film according to any one of claims 1 to 6, wherein only monitoring based on a variable relating to quality is performed. 8. The thermoplastic resin film according to claim 1, wherein at the start of the automatic adjustment of the position, the discharge electrode is once set to a position outside the normal operation range, and the automatic adjustment is performed from the position. Production method. 9. When the automatic adjustment of the position is started, the discharge electrode is temporarily set to a position outside the normal operation range, and the entire discharge electrode is automatically adjusted to the optimum position in the circumferential direction of the cooling rotary drum based on the discharge current. 9. The method for producing a thermoplastic resin film according to claim 8, wherein the direction is adjusted to stop at the optimum position, and then, based on the intensity of the electromagnetic wave, the direction of the discharge electrode is automatically adjusted so as to be parallel to the falling film.